Abstract

Musky Rat-kangaroos, Hypsiprymnodon moschatus, are the smallest member of the kangaroo family (Macropodoidea) and are restricted to Australia's tropical rain forest in north-east Queensland, where they are important dispersal agents for rain forest plants. This study was the first to examine their basic ecology in the field and initially aimed to determine their diet, reproduction, population size and movement patterns. After beginning field-work, I discovered that Musky Rat-kangaroos were primarily frugivorous and scatterhoarded fruits and seeds. Subsequently, the aims of my study focussed on their role as dispersal agents and what effects their caching behaviour had on the survival of the seeds they disperse.

The diet of Musky Rat-kangaroos was examined through direct observation, assessing teeth marks in fruit and by microscopic examination of faeces. They can be classified as frugivores on the basis that the fruits and seeds of at least 49 species accounted for the bulk of their diet throughout the year. However, they also consumed invertebrates and fungus which became more significant in their diet when fruit availability was low. Larger quantities of fungus were consumed during the Wet season (February to April) and invertebrates during the Cold season (May to July) than at other times of year. This shift in emphasis in their diet reflected the pattern of availability of ripe fruits. Ripe fruits were most abundant during the Dry and storm seasons (August to January), declined in the Wet season and reached their yearly minimum in the late Wet and early Cold season (April, May). Fruit biomass was at least 300 times higher during the peak than in the trough periods in the years examined, whereas invertebrate availability was stable in comparison.

Musky Rat-kangaroos were common on my study site, averaging 2.4/ha. They occupied small home ranges (males - 2.1 ha; females 1.4 ha) which overlapped extensively with other individuals of both genders. They were solitary and promiscuous and their seasonal reproductive pattern reflected the changes in availability of ripe fruits. Males underwent rapid expansion of their testes during the peak in fruit availability (September) and remained reproductive until fruit availability declined in March or April. Females evicted pouch young during peak fruit availability (October) and gave birth to one, two or three young at the end of the peak fruiting season (February to April). Both male reproductive seasonality and multiple young per litter are exceptional characteristics among macropodoids and probably result from Musky Rat-kangaroo's unique niche as the only frugivorous macropodoid.

Musky Rat-kangaroos dispersed the seeds of many of the fruits they consumed. They scatterhoarded 14% of the simulated fruits used in an experiment and moved 17% of them further than five metres from their source (up to 68m). The scatterhoarding behaviour of Musky Rat-kangaroos conferred several advantages to two tree species I examined experimentally. Firstly, burial removed their seeds from 100% predation (mostly by rats) suffered by seeds on the litter surface. Secondly, dispersal away from the parent plant aided the survival of one species due to escape from density- or distance-dependent mortality under the parent. Thirdly, 21% of seeds cached by Musky Rat-kangaroos were cached in canopy gaps, a microsite which often increases the vigour of seedlings. Musky Rat-kangaroos killed fewer seeds than many other frugivores sharing their habitat. Because of this, their scatterhoarding behaviour and the low diversity of frugivores in Australia, Musky Rat-kangaroos are clearly of great ecological significance in Australia's tropical rain forests.